I believe the cause to be the turbo bearings going out. To the best of my knowledge (which is somewhat limited on this topic) when they go out the shaft then has a little play in it which as it spins causes the noise. I may be incorrect but that is how I understand it. I just recently got the siren noise after running the guts out of my turbos at an airfield event. They still make and hold boost, but they have the siren sound now.

Not going out, just not perfect and making a little noise. Most people aren't turbo folks and chalk to up to normal turbo noise. A lot do it, some don't. Increasing the boost pressure significantly increases your chances of it happening.

Not going out, just not perfect and making a little noise. Most people aren't turbo folks and chalk to up to normal turbo noise. A lot do it, some don't. Increasing the boost pressure significantly increases your chances of it happening.

Does your car whine? Do you believe it will get worse with time/start to inhibit performance?

Turbos should not I repeat not make that noise, a whistle is 100% normal and with less restrictive exhaust you will hear it more. With a siren or as its called turbo howl your turbos are well on there way to going out. The noise is caused by excessive play in the center section, either in the journal bearings radial play or in the thrust axial play, usually its a combo of both. This allows defelction under boost as the exhaust imparts force on the turbine wheel, the excessive play allows the compressor wheel to actually slightly contact the compressor housing causing metal to metal contact and this noise. Once this occurs it actually starts to machine away the blades of the compressor wheel a little at a time and it will eventually throw itself out of balance, take out the piston rings and everything else with it, and you will start smoking badly. Another thing I have seen with stock turbos is, the turbine side piston ring allowed excessive oil to escape past, which gets under the heat shield and from the extreme heat turns into carbon and as this builds up under the heat shield it pushes the back of the heat shield into the back of the turbine wheel, this can also cause this noise with the same results. Bottom line, turbos are on the way out, next thing in the time line is smoke. Hope this helps.

Turbos should not I repeat not make that noise, a whistle is 100% normal and with less restrictive exhaust you will hear it more. With a siren or as its called turbo howl your turbos are well on there way to going out. The noise is caused by excessive play in the center section, either in the journal bearings radial play or in the thrust axial play, usually its a combo of both. This allows defelction under boost as the exhaust imparts force on the turbine wheel, the excessive play allows the compressor wheel to actually slightly contact the compressor housing causing metal to metal contact and this noise. Once this occurs it actually starts to machine away the blades of the compressor wheel a little at a time and it will eventually throw itself out of balance, take out the piston rings and everything else with it, and you will start smoking badly. Another thing I have seen with stock turbos is, the turbine side piston ring allowed excessive oil to escape past, which gets under the heat shield and from the extreme heat turns into carbon and as this builds up under the heat shield it pushes the back of the heat shield into the back of the turbine wheel, this can also cause this noise with the same results. Bottom line, turbos are on the way out, next thing in the time line is smoke. Hope this helps.

Thanks for the info Tony. It looks like alot of us are in for a suprise

Turbos should not I repeat not make that noise, a whistle is 100% normal and with less restrictive exhaust you will hear it more. With a siren or as its called turbo howl your turbos are well on there way to going out. The noise is caused by excessive play in the center section, either in the journal bearings radial play or in the thrust axial play, usually its a combo of both. This allows defelction under boost as the exhaust imparts force on the turbine wheel, the excessive play allows the compressor wheel to actually slightly contact the compressor housing causing metal to metal contact and this noise. Once this occurs it actually starts to machine away the blades of the compressor wheel a little at a time and it will eventually throw itself out of balance, take out the piston rings and everything else with it, and you will start smoking badly. Another thing I have seen with stock turbos is, the turbine side piston ring allowed excessive oil to escape past, which gets under the heat shield and from the extreme heat turns into carbon and as this builds up under the heat shield it pushes the back of the heat shield into the back of the turbine wheel, this can also cause this noise with the same results. Bottom line, turbos are on the way out, next thing in the time line is smoke. Hope this helps.

What I don't get is how my turbos sound like that with less than 3k on them. I got new turbos under warranty for wastegate issues. I have spent the past month trouble shooting, trying to make absolutely sure the car didn't have some other problem. I just got my DME flashed back to stock, and I will drive it stock through thanksgiving and then I plan to take it in and ask WTF?? I'm thinking they were bad parts from the get-go OR there was an install error.( I actually went back the day after because the car seemed to oscilate- not accelerate smoothly as I left the dealer- they said it was fine) I was afraid that after going back to stock they would quiet down some and then the dealer would tell me nothing is wrong. Happily, the car is now 100% OEM and still sound the same. Combine the sound with boost issues and random limp modes i've been getting....we'll see if the third time is a charm

I will keep the car stock until spring so that if this next set is messed up- I won't have to go through this ordeal AGAIN.

What I don't get is how my turbos sound like that with less than 3k on them. I got new turbos under warranty for wastegate issues. I have spent the past month trouble shooting, trying to make absolutely sure the car didn't have some other problem. I just got my DME flashed back to stock, and I will drive it stock through thanksgiving and then I plan to take it in and ask WTF?? I'm thinking they were bad parts from the get-go OR there was an install error.( I actually went back the day after because the car seemed to oscilate- not accelerate smoothly as I left the dealer- they said it was fine) I was afraid that after going back to stock they would quiet down some and then the dealer would tell me nothing is wrong. Happily, the car is now 100% OEM and still sound the same. Combine the sound with boost issues and random limp modes i've been getting....we'll see if the third time is a charm

I will keep the car stock until spring so that if this next set is messed up- I won't have to go through this ordeal AGAIN.

Install error could cause it, ie, not getting the intake tubes on right and getting something sucked in there. Don't get me wrong I have seen turbos go a LONG time when howling, and I have seen some fail quickly after the noise began. Its not a reason to panic, just know turbos are not supposed to sound like that. Once you start seeing the smoke you know its time to get them swapped. How long that will take is impossible to tell.

My 135i had this siren sound. It only got worse with time. I was FBO and tuned since I got the car new and it wasn't until 15k that I noticed this. Soon it got so loud it was louder than the swoosh sound of the DCI. Always worse when engine was cold but still bad when hot. By 25k it was so loud it was driving me nuts. Still had the sound when reverted back to completely stock. Traded it shortly after that. Now my 2007 335i with 70k (untuned) miles is completley quite. Very faint spool sound when cold. I really think the tune and maybe the other bolt ons (DPs) took their toll. I wonder how long the RB's or Vargas would hold up to the abuse. Hopefully longer than the stock units. Are there any improvement to specifically prevent this syndrome in the upgraded turbos?

My 135i had this siren sound. It only got worse with time. I was FBO and tuned since I got the car new and it wasn't until 15k that I noticed this. Soon it got so loud it was louder than the swoosh sound of the DCI. Always worse when engine was cold but still bad when hot. By 25k it was so loud it was driving me nuts. Still had the sound when reverted back to completely stock. Traded it shortly after that. Now my 2007 335i with 70k (untuned) miles is completley quite. Very faint spool sound when cold. I really think the tune and maybe the other bolt ons (DPs) took their toll. I wonder how long the RB's or Vargas would hold up to the abuse. Hopefully longer than the stock units. Are there any improvement to specifically prevent this syndrome in the upgraded turbos?

Our upgraded thrust option will be able to take a lot more abuse before it starts to wear, and we all know abuse is exactly what upgraded turbos get. Its why people buy them to drive their cars hard, which is why we are taking steps to upgrade the internals to last longer.

My 135i had this siren sound. It only got worse with time. I was FBO and tuned since I got the car new and it wasn't until 15k that I noticed this. Soon it got so loud it was louder than the swoosh sound of the DCI. Always worse when engine was cold but still bad when hot. By 25k it was so loud it was driving me nuts. Still had the sound when reverted back to completely stock. Traded it shortly after that. Now my 2007 335i with 70k (untuned) miles is completley quite. Very faint spool sound when cold. I really think the tune and maybe the other bolt ons (DPs) took their toll. I wonder how long the RB's or Vargas would hold up to the abuse. Hopefully longer than the stock units. Are there any improvement to specifically prevent this syndrome in the upgraded turbos?

Turbos should not I repeat not make that noise, a whistle is 100% normal and with less restrictive exhaust you will hear it more. With a siren or as its called turbo howl your turbos are well on there way to going out. The noise is caused by excessive play in the center section, either in the journal bearings radial play or in the thrust axial play, usually its a combo of both. This allows defelction under boost as the exhaust imparts force on the turbine wheel, the excessive play allows the compressor wheel to actually slightly contact the compressor housing causing metal to metal contact and this noise. Once this occurs it actually starts to machine away the blades of the compressor wheel a little at a time and it will eventually throw itself out of balance, take out the piston rings and everything else with it, and you will start smoking badly. Another thing I have seen with stock turbos is, the turbine side piston ring allowed excessive oil to escape past, which gets under the heat shield and from the extreme heat turns into carbon and as this builds up under the heat shield it pushes the back of the heat shield into the back of the turbine wheel, this can also cause this noise with the same results. Bottom line, turbos are on the way out, next thing in the time line is smoke. Hope this helps.

Wow this sounds pretty bad. But honestly I've been a member of this forum for awhile now and have heard about this siren noise way in the beginning already on 2007 models years ago. If this is in fact so bad, why haven't we heard of any cases of turbos failing yet? This poll points to the majority of users having this noise and multiply that by 5 years worth of 335i users tuning their cars with the majority having experienced this noise for years, yet pretty much no one has had their turbos fail yet from this noise. I'm sure if we dig hard enough there might be 1 or 2 cases but those cases can have other variables as well that caused it. Perhaps its not that bad?

FWIW, I have this noise and it went down alot when i took out the tune or when I installed the stock air box. Do both and I'm pretty sure its quiet again.

Wow this sounds pretty bad. But honestly I've been a member of this forum for awhile now and have heard about this siren noise way in the beginning already on 2007 models years ago. If this is in fact so bad, why haven't we heard of any cases of turbos failing yet? This poll points to the majority of users having this noise and multiply that by 5 years worth of 335i users tuning their cars with the majority having experienced this noise for years, yet pretty much no one has had their turbos fail yet from this noise. I'm sure if we dig hard enough there might be 1 or 2 cases but those cases can have other variables as well that caused it. Perhaps its not that bad?

FWIW, I have this noise and it went down alot when i took out the tune or when I installed the stock air box. Do both and I'm pretty sure its quiet again.

My car is now 100% stock and it sounds the same. I have had the normal spool sound on this car, and another n54 I had- there is a huge difference between that sound (which I think most people are thinking of when they say yes) and the one I'm experiencing.

Turbos should not I repeat not make that noise, a whistle is 100% normal and with less restrictive exhaust you will hear it more. With a siren or as its called turbo howl your turbos are well on there way to going out. The noise is caused by excessive play in the center section, either in the journal bearings radial play or in the thrust axial play, usually its a combo of both. This allows defelction under boost as the exhaust imparts force on the turbine wheel, the excessive play allows the compressor wheel to actually slightly contact the compressor housing causing metal to metal contact and this noise. Once this occurs it actually starts to machine away the blades of the compressor wheel a little at a time and it will eventually throw itself out of balance, take out the piston rings and everything else with it, and you will start smoking badly. Another thing I have seen with stock turbos is, the turbine side piston ring allowed excessive oil to escape past, which gets under the heat shield and from the extreme heat turns into carbon and as this builds up under the heat shield it pushes the back of the heat shield into the back of the turbine wheel, this can also cause this noise with the same results. Bottom line, turbos are on the way out, next thing in the time line is smoke. Hope this helps.

Wow this sounds pretty bad. But honestly I've been a member of this forum for awhile now and have heard about this siren noise way in the beginning already on 2007 models years ago. If this is in fact so bad, why haven't we heard of any cases of turbos failing yet? This poll points to the majority of users having this noise and multiply that by 5 years worth of 335i users tuning their cars with the majority having experienced this noise for years, yet pretty much no one has had their turbos fail yet from this noise. I'm sure if we dig hard enough there might be 1 or 2 cases but those cases can have other variables as well that caused it. Perhaps its not that bad?

FWIW, I have this noise and it went down alot when i took out the tune or when I installed the stock air box. Do both and I'm pretty sure its quiet again.

I'm not going to get into a debate on this. The video posted is NOT a normal turbocharger noise. It indicates a problem. I have heard it hundreds of times. As I said some will go for a while, others will need attention soon after. A whistling sound is totally normal and varies in intensity and pitch. But the video posted was not a normal turbo whistle.

Are you suggesting we try and scam BMW into buying us new turbos because we jammed more than double stock boost through them?

I don't understand why people are surprised by this. You must understand the consequence of what you are doing when you modify a car, especially when you're working at the extremes of stock hardware... e.g. 150-200hp more through the turbos.